title: Kondo screening in high-spin side-coupled two-impurity clusters.
abstract: We study the system of two magnetic impurities described by a two-impurity Kondo model where only the first impurity couples directly to the conduction band, while the second impurity interacts with the first through Heisenberg exchange coupling in a 'side-coupled' configuration. We consider various choices of the impurity spins (S(1)<S(2), S(1)=S(2) and S(1)>S(2)) and we contrast the regimes where the inter-impurity exchange coupling J is either lower or higher than the Kondo temperature T(K)((0)) of the first impurity in the absence of the second. This model is a high-spin generalization of the two-impurity model for side-coupled double quantum dots which corresponds to the simplest S(1)=S(2)=1/2 case, where the moments are Kondo-screened successively in two stages for J<T(K)((0)) (the 'two-stage Kondo effect'). We show that the two-stage Kondo screening occurs generically for S(2)≥S(1). For S(1)≥1, the second Kondo temperature T(K)((2)) is not exponentially reduced, as for S(1)=1/2, but is approximately a power-law function of the coupling J. Furthermore, for S(1)≥1 all three scales (T(K)((0)), J, T(K)((2))) explicitly appear in the temperature dependence of the thermodynamic properties. For S(1)>S(2), there is no second stage of screening for J<T(K)((0)). However, in the opposite limit J>T(K)((0)) the Kondo screening of the effective spin S(1)-S(2) is found.
authors.affiliation: Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia. rok.zitko@ijs.si
authors.forename: R
authors.initials: R
authors.lastname: Žitko